Presently, the basic considerations in the construction of sand screens for oil or water wells are ruggedness of construction, inlet area, resistance to erosion and accuracy of gauge. These considerations are viable as long as the sand screen results in production free from sand. But once production stops due to blockage the sand screen is not functional. Steps must then be taken to alleviate the fluid not passing through the blocked sand screen. The methods presently employed to clean a blocked sand screen are back flushing or pulling the blocked sand screen to the surface, thereby stopping all production of sand-free liquids. Back flushing does not offer a positive means of cleaning because some areas of the sand screen may remain partially blocked thus resulting in a loss of production. Pulling a blocked sand screen is the second method which also results in loss of production due to down time. Thus the purpose of the new rotating washer cleanable sand screen system is to have a system that incorporates the basic considerations in the construction of a sand screen and to have a system that is continually functional through a periodic cleaning. In fact, the new disclosed screen is cleaned by merely rotating a cleaning washer between the coils of the helical spring screen from one end to the other while simultaneously producing filtered liquid through a large opening in the cleaning washer while sliding over a rod from the first end of the screen to its second end. Thus, with a plurality of washers stacked at one end, or the same washer may be passed back and forth any number of times, the screen may be cleaned many times without having to shut the well in for workover, thus saving workover costs and lost production.
There are many thousands of oil wells over the surface of the earth that are drilled and completed in unconsolidated sand, i.e. crumbly sandstone. In such wells, sand does not necessarily precipitate to the bottom of the well, but instead may remain in suspension and may flow up with the oil. As a result, most mechanical parts as valves, bearings, pistons, cylinders, etc. wear out prematurely under such conditions. Accordingly, the sand must be filtered out from the oil, preferably in the well. Petroleum companies have spent large sums of money in trying to find a suitable solution to the sand problem, but heretofore there has been no satisfactory method or long lasting device for preventing the entry of sand into the tube string and eventually into the production tubing and surface tanks.
An oil well foam and wire coil filter is disclosed in U.S. Pat. No. 2,837,032, but that filter is quite sophisticated and expensive to manufacture, and is not adjustable to be opened for backwashing a cleaning liquid, as water, to clean the clogged filter. Another attempted solution was a spring filter as disclosed in U.S. Pat. No. 3,754,651, but because no spacers are apparent between the helical filter elements, the elements would have to be held in slight tension to separate the helical filter elements during filtering. Thus, that filter could not be used as an oil well filter on which high compressive loads may be placed. Likewise, no guide tube or mandrel can be utilized to strengthen the compressive capabilities for converting the filter to one for use in wells. Also, the spring filter of U.S. Pat. No. 3,179,116 is incapable of being strengthened to use in wells. Any compressive force on the triangular spring elements would cause them to collapse, and further the coiled depressions for separating the spring elements would cause the spring elements to flex with a load thereon causing displacement of the adjacent coils and variation of the gauge therebetween.
Accordingly, new and better methods for filtering sand from an oil well, better methods for forming and assembling helical spring sand filters, and better self-cleaning helical spring sand filters are required for mounting on the lower end of a tubing string extending down into a well to the oil containing sand strata.
The disclosed inventions are improvements over those of assignee's U.S. Pat. Nos. 3,901,320 (166-311) and 3,937,281 (166-233).